When an image forming apparatus having an image synthesizing function performs synthesizing processing for overlaying a source pixel on a destination pixel, a transmissivity is designated as one of the parameters. The transmissivity designates a transmission level of a source pixel overlaid on a destination pixel in image synthesizing processing. For instance, when the transmissivity is 100%, a pixel obtained after synthesizing processing is a destination pixel. When the transmissivity is 0%, a pixel obtained after synthesizing processing is a source pixel.
However, in the conventional synthesizing processing, attribute data of a source pixel, overlaid on a destination pixel, is always used as attribute data of a synthesized pixel without taking the transmissivity into consideration. Note that attribute data includes, for instance, the type of object to which the pixel belongs, or the like.
Even in a case where the source pixel and destination pixel have different attributes, the attribute data of the source pixel is always used as attribute data of a synthesized pixel.
In an extreme case, when the transmissivity is set to 100%, a pixel obtained as a result of synthesizing processing has an appearance of the destination pixel, but has an attribute of the source pixel.